(1) Field of the Invention
The present invention relates to a novel cement composition comprising an unsaturated carboxylic acid polymer and a specific alkaline earth metal aluminofluorosilicate glass.
(2) Description of the Related Art
A cement composition comprising an unsaturated carboxylic acid polymer and an alkaline earth metal aluminofluorosilicate glass as main constituents is known as an ionomer cement in which an acid-base reaction caused when both the components are mixed is utilized. This cement composition is cured in a short period in the wet state, and a cured body is obtained having a practically sufficient strength. Therefore, use of this cement composition in various application fields has been examined. Especially, when this cement composition is used as a dental cement, the composition has a high affinity with a hard texture of tooth, and the composition is substantially harmless to a living body. Accordingly, the cement composition is practically used widely as a cavity lining cement for protecting the dental pulp or a filling cement for remedy of a cuneiform defect at a collum dentis.
The alkaline earth metal aluminofluorosilicate glass is generally obtained by pulverizing a bulky glass synthesized by the melting process and is composed of pulverized particles having a particle size of several submicrons to scores of microns (see the published specification of British Patent No. 1,316,129).
When this cement composition is used as a filling cement, since the composition contains large particles as mentioned above, the gloss on the surface of the cured body is poor and an unpleasant touch is given to the tongue of a patient.
In general, a cured body of a cement composition is required to have a strength sufficient to resist an occlusion pressure. Therefore, in the above-mentioned cement composition, in order to improve the strength of the cured body, there is adopted a method in which the content of the alkaline earth metal aluminofluorosilicate glass in the composition is increased.
However, if this method is adopted, the flowability of the conventional cement composition comprising pulverized particles is drastically degraded and the workability is reduced. Therefore, a cement composition providing a cured body having a sufficient strength has not been developed as yet.
When the above-mentioned dental cement composition is used as a dental adhesive material for bonding a metal to tooth, in order to obtain a high adhesion strength, the thickness of the bonding film of the cement composition should be reduced, and therefore, a higher flowability is required than the flowability required when the cement composition is used as a filling cement.
However, in order to obtain a sufficient flowability by using the conventional cement composition comprising pulverized glass particles, it is necessary to reduce the content of the alkaline earth metal aluminofluorosilicate glass in the cement composition, and, therefore, drastic degradation of the strength of the cured body cannot be avoided.
As means for improving the flowability alone, there can be considered a method in which a filler having a spherical shape is used (see the published specification of British Patent No. 1,599,753). However, even if a known spherical filler is used, a cement composition providing a cured body having a sufficient strength cannot be obtained.